1. Field of the Invention
The present invention relates to a multiple pump unit in which a plurality of pumps is arranged in series.
2. Background Art
A multiple pump unit in which a plurality of pumps is arranged in series is widely used as a hydraulic source for operating various actuators in a construction machine and the like.
Japanese Patent No. 3781899, for instance, proposes a multiple pump unit in which a piston pump, a trochoid pump, and a gear pump are coaxially arranged in series.
Specifically, the conventional multiple pump unit includes a pump shaft, a piston pump rotated about an axis line by the pump shaft, a housing main body having an opening that is sized to allow the piston pump to pass therethrough, a port block connected to the housing main body so as to close the opening with the piston pump accommodated in the housing main body, an auxiliary pump shaft connected to the pump shaft in a non-rotatable manner about an axis line, a trochoid pump accommodated in a concave portion formed in the port block and rotated by the auxiliary pump shaft, a gear pump rotated by the auxiliary pump shaft, and a gear pump case connected to the port block so as to surround the gear pump.
Such a multiple pump unit has an advantage that discharged fluids from the piston pump, the trochoid pump, and the gear pump can be independently used in various applications, but has several drawbacks.
For example, the number of pumps to be provided in the multiple pump unit and the number of discharge ports fluidly connected to the pumps functioning as the hydraulic source differ depending on the application to which the multiple pump unit is applied.
That is, in some cases, the piston pump, the trochoid pump and the gear pump all need to be provided, while in other cases, only the piston pump and the gear pump are sufficient to be provided depending on the application.
The number of actuators operated by hydraulic pressure from the trochoid pump also differs depending on the application.
Thus, the number of pumps to be provided and the preferred number of discharge ports for discharging hydraulic pressure from one pump to outside differ according to necessity and/or a specification, but the multiple pump unit described in the above patent document cannot correspond to such various specifications unless the port block itself is replaced.
Furthermore, there is no multiple pump unit, which includes the plurality of pumps, capable of enhancing piping workability of connecting conduits to suction fluid passages and discharge fluid passages of the plurality of pumps.